In the history of golf balls, a thread wound golf ball was firstly developed. The thread wound golf ball is obtained by winding thread rubber in a stretched state on a solid or liquid center to form a thread wound core and covering it with a cover of balata, etc. having a thickness of 1 to 2 mm.
A two-piece solid golf ball was subsequently developed, which was composed of a core formed from integrally molded rubber material and a thermoplastic resin cover (e.g. ionomer resin cover) formed on the core. The two-piece solid golf ball is easily produced because of simple structure, and has excellent rebound characteristics and excellent durability. Therefore, the two-piece solid golf ball is generally approved or employed by many golfers, mainly amateur golfers. However, the two-piece solid golf ball exhibits harder and poorer shot feel at the time of hitting than the thread wound golf ball.
In order to provide a two-piece solid golf ball having a shot feel as good as the thread wound golf ball, a soft type two-piece solid golf ball using a softer core has been proposed. However, the use of the soft core adversely affects on rebound characteristics, thus resulting in a reduction in flight distance and a deterioration in durability.
It has been proposed to place an intermediate layer between the core and the cover of the two-piece solid golf ball to form a three-piece solid golf ball so as to maintain the balance between flight performance and shot feel at the time of hitting. The three-piece solid golf ball generally occupies the greater part of the golf ball market. The three-piece solid golf ball are classified into two types, depending on whether the intermediate layer is formed from rubber material or thermoplastic resin.
For example, a three-piece solid golf ball comprising a two-piece core composed of a core and an intermediate layer, which is formed from vulcanized rubber material having the same composition as the core, is suggested in Japanese Patent Kokai publication Nos. 228978/1990, 332247/1996, 322948/1997, 216271/1998 and the like. These golf balls are characterized by controlling the thickness of the intermediate layer to not less than 1.5 mm, which is relatively thick, and they are classified into two types depending on whether the intermediate layer is harder or softer than the inner core.
In the three-piece solid golf balls described in Japanese Patent Kokai publication Nos. 228978/1990 and 332247/1996, of which the intermediate layer is harder than the inner core, the flight performance is excellent, but the shot feel is poor, because the intermediate layer is thick and hard. Therefore, the golf balls have very soft core in order to accomplish soft and good shot feel. However, in the golf balls, the shot feel when hit by golfers who swing the golf club at low head speed is hard and poor, if the shot feel when hit by golfers who swing the golf club at high head speed is designed to be soft and good. On the other hand, the shot feel when hit by golfers who swing the golf club at high head speed is heavy and poor, if the shot feel when hit by golfers who swing the golf club at low head speed is designed to be soft and good. The golf balls have hard and poor shot feel when hit by a short iron club or putter, if the shot feel when hit by a driver is designed to be soft and good. In addition, the golf balls generally have poor durability.
In the three-piece solid golf balls described in Japanese Patent Kokai publication Nos. 322948/1997 and 216271/1998, of which the intermediate layer is softer than the inner core, the rebound characteristics are largely degraded, which reduces the flight distance when hit particularly by golfers who swing the golf club at low head speed.
Three-piece solid golf balls, of which the intermediate layer is formed from thermoplastic resin, is suggested in Japanese Patent Kokai publication Nos. 313643/1997 and 24084/1995, Japanese Patent Kokoku publication No. 48473/1992 and the like. In the golf balls, the golf ball described in Japanese Patent Kokai publication Nos. 313643/1997, of which the intermediate layer is harder than the inner core, has soft and good shot feel when hit by all golfers who swing at high and low head speed, but has poor shot feel when hit by a short iron club to a putter, when compared with the three-piece solid golf ball having hard type intermediate layer formed from the above vulcanized-rubber.
In the golf balls described in Japanese Patent Kokai publication No. 24084/1995 and Japanese Patent Kokoku publication No. 48473/1992, of which the intermediate layer is softer than the inner core, it is restrained to degrade the rebound characteristics when compared with the three-piece solid golf ball having soft type intermediate layer formed from the above vulcanized rubber. The golf balls have good shot feel when hit by a short iron club to a putter, when compared with the three-piece solid golf ball having hard type intermediate layer formed from the thermoplastic resin. However, since the deformation amount at a portion nearby the surface of the golf ball is large, the area contacted with the golf club, which reduces the spin amount, and the flight distance is long, when compared with the three-piece solid golf ball having hard type intermediate layer formed from the thermoplastic resin. In addition, the shot feel when hit by golfers who swing the golf club at high head speed is heavy and poor.
There has been the case that the conventional three-piece solid golf ball, which has excellent performance for golfers who swing the golf club at high head speed, is not suitable for golfers who swing the golf club at low head speed. On the other hand, there has been the case that the conventional three-piece solid golf ball, which has excellent performance for golfers who swing the golf club at low head speed, is not suitable for golfers who swing the golf club at high head speed. There has been no golf ball, which is suitable for all golfers who swing the golf club at high or low head speed. There has been problem that the conventional three-piece solid golf ball, which has long flight distance and is suitable for golfers who swing the golf club at low head speed, has hard and poor shot feel when hit by an iron club or putter.